It is important for the cornea to be transparent with an optically smooth surface for the formation of a sharp visual image on the retina. The normal, healthy cornea is transparent, mostly acellular connective tissue consisting of collagen fibers and mucopolysaccharides. This tissue is called the stroma, which is covered by several layers of epithelial cells on the exterior surface, while its interior surface is covered with a single layer of endothelial cells. The macromolecules of the stroma form a loosely connected matrix that contains about 80% by weight of aqueous fluid. This interstitial fluid of the stroma is nearly isotonic. The tissue, however, behaves as if it were somewhat dehydrated, since it tends to imbibe, i.e. absorb, additional fluid when immersed in physiological saline. This occurs because the additional osmolality of its macromolecular matrix causes a net flow of water into the stroma by osmosis, with the epithelium acting as a semipermeable membrane. This tendency of water absorption is measured in terms of the so-called “imbibition pressure,” which is about 40-60 torr for the normal cornea. As the degree of hydration of the stroma increases, the imbibition pressure diminishes. Active transport of electrolytes and thus water out of the stroma by its boundary layers of cells keeps the stromal hydration at its normal, i.e. somewhat dehydrated, level in order to maintain its transparency. As the cornea imbibes water, it becomes progressively more cloudy diminishing visual acuity. A highly edematous cornea scatters so much light that it appears to be quite opaque.
Recurrent corneal erosion (RCE) is the recurrence of corneal erosions, either dystrophic or post-traumatic, not precipitated by nor associated with a dry eye condition. RCE can cause the cornea to be edematous. RCE can be a painful and disabling condition of the cornea that causes considerable interference with visual function due to pain, transient decreased vision, and light sensitivity and anxiety, and often results in patients becoming incapacitated and limited in their daily activities. RCE often develops as a result of three different issues: diabetic keratrophy; neurotrophic keratrophy; and following eye surgery such as Lasik surgery.
Symptomatic treatment of RCE with existing hypertonic salt solutions has been ineffective, or even harmful, since the solute of the solution can readily penetrate the stroma achieving hypertonic levels inside the tissue which causes further imbibition of water with the resulting clouding of the cornea which diminishes visual acuity. Additionally, most patients do not respond to treatment with patching or topical lubricants. Some patients may receive temporary relief, but the corneal erosion recurs, resulting in further pain, transient decreased vision, and light sensitivity.
A need therefore exists for an ophthalmic composition that can be used to effectively treat RCE once it has occurred.
A need also exists for an ophthalmic composition that will act as a prophylactic to prevent RCE from occurring, especially for people who are at an increased risk for developing RCE.
A need further exists for packaged ophthalmic solutions that will maintain the stability of ophthalmic compositions for preventing and treating RCE.